Device for solar-powered water purification in the offing

Washington: An Indian-origin scientist in US has designed a device that can sanitise dirty water merely by absorbing sunlight, an advance that could be a global game-changer in the potable water crisis.

Venkat Viswanathan, assistant professor at the Carnegie Mellon University in US, along with colleagues designed a conceptual device which would combine with unsanitary water and sunlight to create a potable water source.

"Theoretically, you would dip a stick of this material in a bucket of water, take it outside, and it would absorb sunlight," said Viswanathan.

"What we are doing, essentially, is using the energy of the Sun to excite or oxidise water into a compound that has the potency to clean," he said.

The proposed device consists of a rod of some material, ideally tin oxide or titanium dioxide, which would absorb sunlight to allow the water to oxidise, generating hydrogen peroxide.

Tin oxide and titanium dioxide are very stable compounds. In other words, they do not like to bond; hardly any chemicals stick to them.

That property of binding so weakly to other compounds causes the formation of hydrogen peroxide. Using energy from the solar photons, tin oxide and titanium oxide oxidise the water molecule (H2O) to hydrogen peroxide (H2O2).

Then, once the hydrogen peroxide has eliminated all of the water's bacteria and organic pollutants, the device would self-shut down - when it runs out of things to clean, hydrogen peroxide is unstable in water.

"And once the catalytic reaction has finished, you would take the stick out and expose the water to sunlight for a little bit longer. If the water heats up even just a little bit, the hydrogen peroxide will decompose and become water and oxygen again," Viswanathan said.

It is predicted that about 3 billion people would not have access to clean drinking water by 2020, Viswanathan said, but he is hopeful that the device, when it is eventually prototyped and released, will bring that number down.

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